The fact that all observers measure the same speed for any light signal (passing through a vacuum) can be used to derive the Lorentz transformation rules in various ways.

### The Ship’s Mast

Consider a flashlight or laser pointer shining from the crow’s nest at the top of a ship’s mast down to a point on the deck right at the base of the mast

### The Light Clock

If each observer measures time using a clock whose ticks are triggered by the reflection of a light pulse back and forth between two reflecting plates

### The Wave Front Formula

The condition that the position of the light signal is given by the same formula in terms of either observer’s coordinates